so as the title states. when i rev my engine the tach zeros out briefly then comes up to where its supposed to be.found one bad wire so i fixed that. seems like i have a little hesitation and underpowered. new coil (msd) also have a new msd box. does the same whether i use stock ignition or msd.

what do you guys think?

ecm?
bad pick up coil?

 

The MSD box can cause all sorts of errors. I had to put a 10K resistor inline with my tach wire to get it to work properly. You can also use the MSD tach adapter.

Although if it does it with the stock ignition and coil then i would look into the resistor network on the tach,

 

so where would i start? the white wire going into the harness had a bad spot in it so i had to repair it.

 

I would start by getting the tach working with the stock ignition. Check the rest of the wiring. Then if that is good remove the cluster and check the resistor network on the tach.

 

the tach works normally. just if i hit the gas really fast it will go to zero for a second then jump to where its supposed to be. like it stutters before coming up. the motor revs normally. sounds like i has a slight miss at idle. but it still not fully broke in either.

 

found this on msd's site. is there a tach filter for the gm small caps? i have my msd hooked up with their adapter making it plug and play. they say the tach '0'ing out could be due to the tach filter

Note #3: General Motors Corporation vehicles have an inline filter that should be bypassed when the factory tachometer drops back to zero as the engine RPM is going up. The drawings at the right show what the filter might look like. Located the filter by tracing the wire from the Tach Terminal on Vehicles equipped with an HEI Ignition system. On vehicles equipped without an HEI, trace the wire from the coil negative terminal until the filter is found. Disconnect both wires from the filter and leave disconnected. Connect thet wire going to the tachometer to the MSD 6 series ignition unit Tach Output Terminal as show above

 

Right but you said it also does it with stock stuff.

 

My tach used to drop out over 5k RPM at full throttle. I put the MSD tach filter in and now it's fine. I'll post the part # when I get home.

The problem if I remember right, is the dual sync dizzy couldn't power both the MSD ignition box and the tach gauge so it needed a signal booster/filter.

 

yeah thats what ive been reading. ive also read that you have to use the grey wire off the box straight to the white connector. sucks for me since the pin for my connector is pushed inside the ox and msd wont repair it cause i bought it off fleabay and dont have an actual receipt. so i have to figure out how to open up the box.

 

issue fixed. repaired my msd myself. ran grey wire from box to white wire feeding tach. car runs better that ever. also fixed my egr solenoid i had routed backwards.